A shaft furnace is a furnace whose geometrical basic shape is “shaft-like”. Typically, the height of shaft furnaces greatly exceeds their width and their depth. The basic shape of a shaft furnace often corresponds to a hollow cylinder, a hollow cone or a combination of both shapes. It is normally the case that combustion, reduction and melting processes occur in a shaft furnace, wherein the gases that are generated in the furnace rise upward. Shaft furnaces are utilized either for heating purposes or serve as a metallurgical plant for the generation of pure metals from ores, for the further processing of the metals, or for the production of other materials.
A special type of shaft furnaces are blast furnaces by means of which it is possible to produce liquid metal, normally raw iron, from ores in a continuous reduction and melting process. In relation to conventional shaft furnaces, blast furnaces place particular demands on the type of construction of the furnace, and in particular on the internal lining and cooling thereof, owing to the specific demands placed on the smelting of ores.
Blast furnaces are normally used as part of a complete integrated smelting works. Aside from the furnace itself, a blast furnace plant comprises, for example, transport devices for the filling (“feeding”) of the blast furnace with input materials (e.g. iron ore and additives) and with reducing agents or energy carriers (e.g. coke) and devices for the extraction or discharging of the substances that form in the blast furnace (e.g. raw iron, slag, exhaust gases).
In many shaft furnaces, and in particular in blast furnaces, gases are introduced into the furnace from the outside in order to permit or influence the reactions taking place in the furnace. The gases may for example be air or pure oxygen. Devices for the injection of the gases commonly comprise ring lines which run around the furnace and which have multiple tuyeres or nozzles leading into the furnace interior and which additionally have lances that also lead into the furnace interior.
DE 101 17 962 B4 has disclosed, for example, a method for the thermal treatment of raw materials and a device for carrying out said method. The described device is a cupola furnace. Cupola furnaces are likewise shaft furnaces in which metals can be melted. By contrast to blast furnaces, cupola furnaces normally serve for the production of cast iron from raw iron and scrap metal, and accordingly differ from blast furnaces in terms of mode of operation and structural form.
In DE 101 17 962 B4, it is proposed that, in addition to an injection of air, gases with different oxygen content be alternatively introduced into the furnace. Said gases may be air and pure oxygen. For this purpose, two separate ring lines are led around the furnace. The first ring line is always filled with air, whereas the second ring line is alternatively filled with different gases (e.g. oxygen). Through the targeted introduction of gases with different oxygen content, it is the intention to control the reactions and in particular the temperatures in the furnace.
The solution presented in DE 101 17 962 B4 has the disadvantage of a cumbersome construction with multiple separate ring lines. Furthermore, the solution described in DE 101 17 962 B4 is restricted to cupola furnaces.
EP 1 948 833 B1 has disclosed a method for operating a shaft furnace. Said shaft furnace may be a cupola furnace or a blast furnace. In the solution described in EP 1 948 833 B1, too, it is proposed that a treatment gas, for example oxygen, be injected into the furnace.
It is the intention for the injected gas to be modulated in pulsed fashion. This means that, proceeding from a low base pressure, the pressure of the injected gas is briefly increased at time intervals. By way of this approach, it is sought to achieve better gas propagation in the furnace.
The solution described in EP 1 948 833 B1 has the disadvantage that, outside the “raceway”, no reaction improvements, or only minor reaction improvements, are attained.